Nickel alloy with good stress-rupture strength

ABSTRACT

A HARDENABLE NICKEL ALLOY CONTAINING SPECIAL PERCENTAGES OF CHROMIUM, ALUMINUM TITANIUM HALFNIUM, YTTRIUM, MOLYBDENUM, TUNGSTEN, CARBON ECT., OFFERS ENCHANCED STRESS RUPTURE STRENGTH OVER THE INTERMEDIATE TEMPERATURE RANGE OF 600*C-900*C. WHILE RETAINING A SATISFACTORY LEVEL OF DUCTILITY.

3,832,167 NICKEL ALLOY WITH GOOD STRESS-RUPTURE STRENGTH 3,832,167 Patented Aug. 27, 1974 Within the ranges above given, preferred alloys of the invention are those in which one or more elements are maintained within the following ranges: 0.03% to 0.2% carbon; to 13% chromium; up to 12% tungsten; up

St Waller h Sutton coldfield! 3 Nlgel 5 to 5% tantalum; up to 5% titanium; 4.5 to 7% alumi Anthony t Bnlmmgham England asslgnors i? num; 0.02% to 0.7% zirconium, and up to 0.03% boron. 3 Imemammal Nickel Company New Yo: A particularly preferred group of alloys contain from e Feb. 22 1972 Ser. No. 228 294 0.03% to 0.2% carbon; from 5% to 13% chromium; up cl is isizii g iicaeon Gi'eat Bi'itain, Feb. 23, 1971, to 20% cobalt; up to 8%, a t 7%, molybdenum;

71 10 up to 12% tungsten; up to 4% IllOblllII'l, up to 5% tanta- Int. Cl. C22c 19/00 lum; up to 5% titanium; from 4.5% to 7% aluminum; US. Cl. 75-170 4 Claims from 0.02% to 0.2% zirconium; up to 0.03%, e.g., 0.001% to 0.01%, boron; 0.008% to 0.08% yttrium; 0.3% to URE 1.5% hafnium; balance, apart from impurities, being ABSTRACT OF THE DISCLOS nickel in an amount of at least 50%.

A hardenable ni k l ll y containing Speclal P fw Further classes of preferred alloys of the invention are of chromium, aluminum, titanium, hafnium, yttrium, those f any of the above groups containing up to molybdenum, tungsten, carbon, etc., offers enhanced stress molybdenum and f to tungsten and those rupture strength over the intermediate temperature range containing f o to 7% molybdenum and up to 5% of 600 C.900 C. while retaining a satisfactory level of 20 tungsten. ductility. In carrying the invention into practice, the alloys in accordance herewith should normally be produced by As is generally recognised in the art, Over the past vacuum melting, for example, in a vacuum induction years considerable emphasis has been given to the develfurnace, followed by addition of the hafnium and yttrium opment of the so-termed superalloys, notably those of the 5 (or lanthanum) and casting, either under vacuum or unnickel-base precipitation hardenable type, capable of der an inert atmosphere. In striving for optimum charmeeting the stringent requirements demanded by various acteristics, the alloys can be subjected to vacuum refining commercial applications. As an example of this, mention before the yttrium and hafnium additions are made, for might be made of the gas turbine engine, particularly example by vigorously agitating the molten alloy in a such components as stator and rotor blades intended to vacuum induction furnace for an extended period of operate over the intermediate temperature range of time, e.g. from 15 to 60 minutes at a temperature of 1400 600 C.900 C. as well as at higher levels. A primary to 1600 C., preferably about 1500 C., and at a pressure aim recently has been to overcome or minimize the not exceeding 100 microns, preferably not exceeding 10 trough ductility problem within this temperature range microns and more preferably not exceeding 2 microns, and thereby extend the overall usefulness of a given comadding the yttrium and hafnium, and casting the melt. ponent. Tensile ductility remains an important con- A preferred vacuum refining operation is effected in a sideration herein, but the subject invention is addressed vacuum induction furnace for about 30 minutes under a principally to the task of also effecting over the 600 C.- pressure of about 1 micron with the crucible set wholly 900 C. range an improved level of stress rupture strength Within the furnace induction coil and being between one in respect of nickel alloys hereindescribed. and two thirds filled with melt so that the upper part of It has now been found that certain precipitation hardthe coil is above the normal level of melt in the crucible. enable, nickel alloys containing special percentages of When the furnace is in operation, this arrangement inchromium, aluminum, titanium and other constituents as creases the intensity of agitation to which the melt is subdescribed herein, offer enhanced stress-rupture strengths i If desired the Yttrium and hafnium y he added in combination with adequate ductility, tensile strength, under an inert atmosphere, -gargon, at a moderate etc., when hafnium and yttrium are co-present in pre- Pressure example, 100 of yscribed percentages. The present invention results primarily in improvement Accordingly, alloys contemplated herein contain (by in stress-rupture strength, although over generally the weight) up to 20%, e.g., 2% to 20%, chromium; from whole of the above-defined base composition range marked 3% to 8% aluminum, up to 8% titanium, the sum of the improvement is also obtained in the intermediate temperaluminum plus titanium being from 4% to 12%; from a llre tens e ductility. 0.25% to 3% hafnium; from 0.005% to 0.15% yttrium; To illustrate the improved properties obtained, yttrium up to 20% cobalt; up to 20% tungsten; up to 3% iron; and hafnium were incorporated, separately and together up to 8% molybdenum; up to 9% tantalum; up to 4% into two alloys of the following compositions:

Composition (percent by wt.)

Alloy C Cr C0 Mo W Nb Ta Al Ti Zr B Ni 1 0.13 5.8 2 ..0.14 9.1 3.2.33. 1.9' 1.5'8Ii 0% i:

niobium; up to 1.5% vanadium; up to 1.5%, e.g., 0.01%

to 0.5%, zirconium; up to 0.3%, e.g., 0.001% to 0.1%, A 35 kg. heat of each alloy was made in a kg. ca-

boron; up to 0.3% carbon; up to 0.5% manganese; up to pacity 3 kc./s. vacuum induction furnace and cast as 10 0.3% silicon, and the balance, other than impurities, being 6 kg. sticks which were cut into 4 kg. portions and reessentially nickel, the nickel being at least 30% and 5 melted in a 4 kc./s. vacuum induction furnace of 10 kg.

preferably at least 50%. Advantageously the chromium capacity. Various amounts of yttrium and hafnium singly percentage does not exceed 14.5% and the yttrium conand together were added to the 4 kg. melts under argon tent does not exceed 0.1%. Most advantageously, the perat a pressure of 100 mm. of mercury and each of the recentages of hafnium and yttrium are from 0.3% to 1.5 sulting melts was cast into a preheated refractory mould and from 0.008% to 0.08%, respectively. The yttrium can, if desired, be partly or wholly replaced by a similar amount of lanthanum.

to provide suitably tapered test piece blanks. A blank melt with no addition was similarly cast to provide a reference sample.

Suitable test bars were machined from the tapered test blanks and were subjected to short-time tensile tests and given by way of example in the following Table II in percent by weight.

TABLE II Mo W Nb Ta Ti to stress-rupture tests, all at 760 C. The results are set forth in the following Table I.

TABLE I Stress-rupture properties at Tensile properties at 760 C. 65 Mar/760 C. Analysed contents Elonga- Elonga- Alloy RA. U.T.S. Life tion No. Ht Y (percent) (percent) (hbar) (h.) (P rcent) NoTE.R.A.=Reduction in area; U.T.S.=Ultimate tensile stress.

It will be seen that while the separate additions of hafnium and yttrium improved the stress-rupture life and ductility of each of the alloys to some extent, a substantial and unexpected further increase in the stress-rupture life resulted from the combined addition. The tensile ductility of the alloys containing both yttrium and hafnium was also improved compared with the alloys with no additions.

The results in Table I also show that a very satisfactory combination of stress-rupture and tensile properties, including tensile ductility, is exhibited by alloys containing less than 1.5% hafnium, when yttrium is also present.

A further advantage of the co-presence of yttrium with hafnium is that it refines the grains of the castings. This is advantageous when making castings of heavy section, e.g. 2.5 cm. or more, and particularly in the case of castings having both thin and thick sections such as automobile gas turbine rotors with integrally cast blades. In such castings a fine grain structure can thus be obtained in the heavy centre section as well as the thin blade sections.

The compositions of other alloys of which the stressrupture strength can be improved by the incorporation of yttrium and hafnium in accordance with the invention are Castings produced from the alloys in accordance herewith can be employed in automotive and aircraft turbine engine blades, and also as dies, turbine rotors, etc., particularly within the temperature range of 600 C.-900 C. and particularly with regard to cast low chromium, highly precipitation hardened nickel superalloys.

Although, the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A high nickel superalloy in the cast condition and characterized by good stress-rupture strength together with satisfactory ductility over the temperature range of 600 C.-900 C., the alloy consisting of up to 20% chromium, about 4.5% to 8% aluminum, up to 8% titanium, the sum of the aluminum plus titanium not exceeding 12%, about 0.25% to 3% hafnium, about 0.005% to 0.1% yttrium, up to 20% cobalt, up to 20% tungsten, up to 8% molybdenum, up to 3% iron, up to about 5% tantalum, up to 4% niobium, up to 1.5% vanadium, up to 1.5 zirconium, up to 0.3% boron, up to 0.3% carbon, up to 0.5% manganese, up to 0.3% silicon, and the balance essentially nickel, the nickel being present in an amount of at least about 30%, said casting being further characterized in that it exhibits grain refinement over the same alloy free of hafnium and yttrium whereby the casting is rendered more suitable for use in thick sections.

2. A cast nickel alloy in accordance with claim 1 containing about 0.3% to 1.5 hafnium and 0.008% to 0.08% yttrium.

3. A cast nickel alloy in accordance with claim 1 containing from 5% to 13% chromium, about .03% to 0.2% carbon, about 4.5 to 7% aluminum, up to about 0.03% boron, 0.66% to 1.65% hafnium, 0.01% to 0.08% yttrium, 2% to 7% molybdenum and up to 5% tungsten.

4. A cast nickel alloy in accordance with claim 1 containing up to 4% molybdenum and 6% to 12% tungsten.

References Cited UNITED STATES PATENTS 3,653,987 4/1972 Bocsch -l7l 3,526,499 9/1970 Quigg et a1. 75-171 3,677,331 7/1972 Lund et a1. 75-171 3,667,938 6/1972 'Boesch 75l71 RICHARD O. DEAN, Primary Examiner US. Cl. X.R. 

